1. Field of the Invention
The present invention relates to a process for manufacturing a tyre for vehicle wheels. In a further aspect, the invention relates to a tyre for vehicle wheels obtained through said process.
In more detail, the present invention relates to the manufacture of a substantially airtight coating layer, typically referred to as “liner” that is usually provided on the radially internal surface of a tyre of the “tubeless” type, i.e. a tyre in which an air tube is not present, to ensure hermetic seal to the inflating gases of the tyre under use conditions.
2. Description of the Related Art
In traditional building processes, in which the tyre is obtained through assembly of semifinished products on a building drum, the liner is usually formed by winding up a sheet of raw elastomeric material around the outer surface of the building drum, which sheet extends over the whole width of a carcass sleeve subsequently formed following application of the carcass ply/plies and of the annular anchoring structures engaged to the end flaps of the carcass ply/plies.
There are also building processes in which the tyre components are made by laying a plurality of elementary components on a forming drum so as to avoid the need for intermediate steps in order to work and store the semifinished products.
In the present context by “elementary components” it is intended continuous elongated elements of elastomeric material, strip-like elements, i.e. ribbon-like elements of elastomeric material cut to size and reinforced with at least two textile or metallic cords parallel to each other in the longitudinal direction of the element itself, rubberised textile or metallic cords.
Here and in the following of the present specification, by low-section tyre it is intended a tyre having a reduced section ratio, i.e. wherein the section height measured between the radially outermost point of the crown structure and the radially innermost point of the bead, is lower than about 50% of the section width axially measured at the point of maximum chord of the tyre. More specifically, the low-section tyres taken into account in the present context are those in which the section height is included between about 20% and about 50% of the section width.
Document WO 2008/099236 in the name of the same Applicant illustrates manufacture of the liner by spiralling, i.e. through dispensing of at least one continuous elongated element of elastomeric material on the outer surface of a substantially cylindrical building drum driven in rotation around its geometric axis so as to determine laying of the continuous elongated element into a plurality of coils disposed close to each other and/or in superposed relationship in order to generate a continuous layer on said outer surface. Then a radial expansion is imposed to the carcass structure made in a cylindrical conformation on the building drum, so as to give it a toroidal conformation for coupling to an outer ring previously positioned around it.
Document JP 2005-153348 illustrates manufacture of the liner through winding of a sheet of elastomeric material with a constant thickness around the outer surface of a cylindrical drum, which sheet has been obtained beforehand by calendering, and cut to size according to the circumferential extension of the drum itself. Disposed in the continuation of the axially opposite ends of the central portion are two axially external portions obtained by spiralling of a continuous elongated element of elastomeric material on the cylindrical drum.